ApoE4 reduction: an emerging and promising therapeutic strategy for Alzheimer's disease

Suppression of CNS APOE4 Expression by miRNAs Delivered by the S2 AAVrh.10 Capsid-modified AAV Vector

The homozygous APOE4 genotype is the major risk factor for the development of early Alzheimer's disease. Genome engineering studies in mouse models of human APOE4-dependent pathology have established that reduction of APOE4 expression can rescue the phenotype. We hypothesized that APOE4 could be suppressed in the CNS of APOE4 homozygotes using adeno-associated virus (AAV) expression of microRNAs (miRNA) designed to hybridize to APOE mRNA. We screened 9 different miRNAs targeting APOE following transfection in HEK293T and Huh7 cells. Optimal APOE suppression was obtained with mir2A (targeting coding region nt330-351) and mirN4 (3' untranslated region nt1142-1162). miRNA expression cassettes were designed with two copies of each of these two miRNAs co-expressed with a mCherry transgene. To optimize delivery of these miRNAs, an engineered AAVrh.10 variant was identified from a screen of multiple peptide insertions into capsid loop IV and substitutions in loop VIII. This led to identifying the AAV.S2 capsid with enhanced transduction of both neurons and glia and enhanced distribution in the brain. The engineered capsid was used to deliver the APOE miRNA suppression cassette to the hippocampus of TRE4 mice (human APOE4 knock-in replacement of the murine apoE locus). Two weeks after intra-hippocampus administration, regional expression of miRNA at the injection site was quantified at the mRNA level relative to an endogenous reference. The AAV.S2 capsid provided 2.31 ± 0.37-fold higher expression of miRNA over that provided by AAVrh.10 (p<0.05). In the targeted region, a single intra-hippocampus AAV.S2 administration suppressed hippocampal APOE4 mRNA levels by 76.5 ± 3.9% compared to 41.3 ± 3.3% with the same cassette delivered by the wildtype AAVrh.10 capsid (p<0.0001). We conclude that an expression cassette with two different miRNAs targeting APOE4 delivered by the AAV.S2 capsid will generate highly significant suppression of APOE4 in the CNS.

New insights into innate immunity in Alzheimer's disease: from APOE protective variants to therapies

Recent discoveries of rare variants of human APOE may shed light on novel therapeutic strategies for Alzheimer's disease (AD). Here, we highlight the newly identified protective variant [APOE3 Christchurch (APOE3ch, R136S)] as an example. We summarize human AD and mouse amyloidosis and tauopathy studies from the past 5 years that have been associated with this R136S variant. We also propose a potential mechanism for how this point mutation might lead to protection against AD pathology, from the molecular level, to cells, to mouse models, and potentially, to humans. Lastly, we extend our discussion of the recent insights gained regarding different APOE variants to putative therapeutic approaches in AD.

The Possible Associations between Tauopathies and Atherosclerosis, Diabetes Mellitus, Dyslipidemias, Metabolic Syndrome and Niemann-Pick Disease

Clinical evaluation and treatment of tauopathic syndromes remain a challenge. There is a growing interest in theories concerning their possible associations with metabolic diseases. The possible connection between those diseases might be linked with cerebrovascular dysfunction. The endothelial cell damage and impairment of the blood-brain barrier observed in atherosclerosis or diabetes may play a role in contributing to tauopathic syndrome development. Additionally, the inflammation evoked by pathological metabolic changes may also be involved in this process. Multiple cases indicate the coexistence of metabolic disorders and tauopathic syndromes. These findings suggest that modifying the evolution of metabolic and cerebrovascular diseases may impact the course of neurodegenerative diseases. Obtained data could indicate the possible benefits of introducing routine carotid artery sonography, revascularization operation or antihypertensive medications among patients at high risk for tauopathies. This review has identified this understudied area, which is currently associated with several diseases for which there is no treatment. Due to the pathomechanisms linking metabolic diseases and tauopathies, further investigation of this area of research, including cohort studies, is recommended and may provide new pharmacological perspectives for treatment.

Phytotherapy in Alzheimer's Disease-A Narrative Review

Alzheimer's disease (AD) affects 50-70% of patients with dementia, making it the leading cause of dementia. The condition is classified as a neurodegenerative, progressive and incurable disease. The disease is affecting more and more people around the world. AD has a multifactorial nature, spreading from beta-amyloid deposition to inflammation in patients' brains. Patients experience cognitive impairment and functional decline. Although it is a disease that occurs mainly in the elderly, it is increasingly being diagnosed in young people between the ages of 30 and 40. It not only affects the patient themself but also reduces the quality of life of their closest caregivers. According to the WHO, the treatment of AD consumes USD 1.3 trillion globally, but it is only symptomatic, as there are no drugs to prevent the onset of AD or treat the cause of its onset. Due to the numerous side effects of therapy and the lack of proactive drugs that act on the pathomechanism of AD, alternative therapies are being sought. One possible option that has many studies confirming its effect is phytotherapy. Many herbs have pharmacological properties, such as antioxidant, anti-inflammatory, or neuroprotective effects, making them the future of cognitive disorders and AD treatment. This review focuses on some of the most promising herbs that have potentially potent properties and effects in AD therapy. These include Curcuma longa, Panax ginseng, Berberis and Crocus sativus. These herbs may perhaps be key in the future to make functioning and life easier for patients struggling with AD.

Reelin links Apolipoprotein E4, Tau, and Amyloid-β in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder that affects the cerebral cortex and hippocampus, and is characterised by progressive cognitive decline and memory loss. A recent report of a patient carrying a novel gain-of-function variant of RELN (H3447R, termed RELN-COLBOS) who developed resilience against presenilin-linked autosomal-dominant AD (ADAD) has generated enormous interest. The RELN-COLBOS variant enhances interactions with the apolipoprotein E receptor 2 (ApoER2) and very-low-density lipoprotein receptor (VLDLR), which are associated with delayed AD onset and progression. These findings were validated in a transgenic mouse model. Reelin is involved in neurodevelopment, neurogenesis, and neuronal plasticity. The evidence accumulated thus far has demonstrated that the Reelin pathway links apolipoprotein E4 (ApoE4), amyloid-β (Aβ), and tubulin-associated unit (Tau), which are key proteins that have been implicated in AD pathogenesis. Reelin and key components of the Reelin pathway have been highlighted as potential therapeutic targets and biomarkers for AD.

The potential anti-Alzheimer's activity of Oxalis corniculata Linn. Methanolic extract in experimental rats: Role of APOE4/LRP1, TLR4/NF-κβ/NLRP3, Wnt 3/β-catenin/GSK-3β, autophagy and apoptotic cues

ETHNOPHARMACOLOGICAL RELEVANCE

Oxalis corniculata (O. corniculata) is a member of Oxalidaceae family, widely distributed in Asia, Europe, America, and Africa, used extensively as food and its traditional folkloric uses include management of epilepsy, gastric disorders, and neurodegenerative diseases, together with its use in enhancing health. Numerous pharmacological benefits of O. corniculata are linked to its anti-inflammatory and antioxidant abilities. One of the most prevalent neurodegenerative disorders is Alzheimer's disease (AD) in which neuroinflammation and oxidative stress are its main pathogenic processes.

AIM OF THE STUDY

Our research aimed to study the neuroprotective effect of the methanolic extract of Oxalis corniculata Linn. (O. corniculata ME), compared to selenium (Se) against AlCl3-induced AD.

MATERIALS AND METHODS

Forty male albino rats were allocated into four groups (Gps). Gp I a control group, the rest of the animals received AlCl3 (Gp II-Gp IV). Rats in Gp III and IV were treated with Se and O. corniculata ME, respectively.

RESULTS

The chemical profile of O. corniculata ME was studied using ultraperformance liquid chromatography-electrospray ionization-quadrupole time-of-flight mass spectrometry, allowing the tentative identification of sixty-six compounds, including organic acids, phenolics and others, cinnamic acid and its derivatives, fatty acids, and flavonoids. AlCl3 showed deterioration in short-term memory and brain histological pictures. Our findings showed that O. corniculata ME and selenium helped to combat oxidative stress produced by accumulation of AlCl3 in the brain and in prophylaxis against AD. Thus, Selenium (Se) and O. corniculata ME restored antioxidant defense, via enhancing Nrf2/HO-1 hub, hampered neuroinflammation, via TLR4/NF-κβ/NLRP3, along with dampening apoptosis, Aβ generation, tau hyperphosphorylation, BACE1, ApoE4 and LRP1 levels. Treatments also promoted autophagy and modulated Wnt 3/β-catenin/GSK3β cue.

CONCLUSIONS

It was noted that O. corniculata ME showed a notable ameliorative effect compared to Se on Nrf2/HO-1, TLR4/NF-κβ/NLRP3, APOE4/LRP1, Wnt 3/β-catenin/GSK-3β and PERK axes.

The role of ATP-binding cassette transporter G1 (ABCG1) in Alzheimer's disease: A review of the mechanisms

The maintenance of cholesterol homeostasis is essential for central nervous system function. Consequently, factors that affect cholesterol homeostasis are linked to neurological disorders and pathologies. Among them, ATP-binding cassette transporter G1 (ABCG1) plays a significant role in atherosclerosis. However, its role in Alzheimer's disease (AD) is unclear. There is inconsistent information regarding ABCG1's role in AD. It can increase or decrease amyloid β (Aβ) levels in animals' brains. Clinical studies show that ABCG1 is involved in AD patients' impairment of cholesterol efflux capacity (CEC) in the cerebrospinal fluid (CSF). Lower Aβ levels in the CSF are correlated with ABCG1-mediated CEC dysfunction. ABCG1 modulates α-, β-, and γ-secretase activities in the plasma membrane and may affect Aβ production in the mitochondria-associated endoplasmic reticulum (ER) membrane (MAM) cell compartment. Despite contradictory findings regarding ABCG1's role in AD, this review shows that ABCG1 has a role in Aβ generation via modulation of membrane secretases. It is, however, necessary to investigate the underlying mechanism(s). ABCG1 may also contribute to AD pathology through its role in apoptosis and oxidative stress. As a result, ABCG1 plays a role in AD and is a candidate for drug development.

Cell subtype-specific effects of genetic variation in the Alzheimer's disease brain

The relationship between genetic variation and gene expression in brain cell types and subtypes remains understudied. Here, we generated single-nucleus RNA sequencing data from the neocortex of 424 individuals of advanced age; we assessed the effect of genetic variants on RNA expression in cis (cis-expression quantitative trait loci) for seven cell types and 64 cell subtypes using 1.5 million transcriptomes. This effort identified 10,004 eGenes at the cell type level and 8,099 eGenes at the cell subtype level. Many eGenes are only detected within cell subtypes. A new variant influences APOE expression only in microglia and is associated with greater cerebral amyloid angiopathy but not Alzheimer's disease pathology, after adjusting for APOEε4, providing mechanistic insights into both pathologies. Furthermore, only a TMEM106B variant affects the proportion of cell subtypes. Integration of these results with genome-wide association studies highlighted the targeted cell type and probable causal gene within Alzheimer's disease, schizophrenia, educational attainment and Parkinson's disease loci.

A new andrographolide derivative ADA targeting SIRT3-FOXO3a signaling mitigates cognitive impairment by activating mitophagy and inhibiting neuroinflammation in Apoe4 mice

BACKGROUND

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases and mitophagy deficit was identified as the typical abnormality in early stage of AD. The neuroprotective effect of andrographolide (AGA) has been confirmed, anda acetylated derivative of AGA (3,14,19-triacetylandrographolide, ADA) was considered to have stronger efficacy.

PURPOSE

The current study aims to investigate the impact of ADA on cognitive ability in a sporadic AD model and explore its potential mechanism.

STUDY DESIGN/ METHODS

Apoe4 mouse was adopted for evaluating the impact of AGA on cognitive impairment through a serious of behavioral tests. The molecular mechanism of ADA involved in mitophagy and neuroinflammation was investigated in detailby Western blot, ELISA, immunofluorescence and transmission electron microscopy in Apoe4 mice, as well as Apoe4-transfected BV2 cells and HT22 cells.

RESULTS

ADA application significantly improved cognitive impairment of Apoe4 mice, and lessened Aβ load and neuronal damage, which has stronger activity than its prototype AGA. Accumulated mitophagy markers LC3II, P62, TOM20, PINK1 and Parkin, and decreased mitophagy receptor BNIP3 in hippocampus of Apoe4 mice were greatly reversed after ADA treatment. Meanwhile, ADA promoted the recruitment of BNIP3 to mitochondria, and the transport of damaged mitochondria to lysosome, indicating that disturbed mitophagy in AD mice was restored by ADA. Inhibited SIRT3 and FOXO3a in Apoe4 mice brains were elevated after ADA treatment. ADA also lightened the neuroinflammation caused by NLRP3 inflammasome activation. Additionally, damaged mitophagy and/or activated NLRP3 inflammasome were also observed in BV2 cells and HT22 cells transfected with Apoe4, all of which were rescued by ADA incubation. Noteworthily, SIRT3 inhibitor 3-TYP could abolish the impact of ADA on mitophagy and NLRP3 inflammasome in vitro.

CONCLUSION

ADA exerted stronger cognition-enhancing ability in relative to AGA, and ADA could repaire mitophagy deficiency via SIRT3-FOXO3a pathway, and subsequently inhibite NLRP3 inflammasome to mitigate AD pathology.

Complement-mediated synapse loss in Alzheimer's disease: mechanisms and involvement of risk factors

The complement system is increasingly recognized as a key player in the synapse loss and cognitive impairments observed in Alzheimer's disease (AD). In particular, the process of complement-dependent synaptic pruning through phagocytosis is over-activated in AD brains, driving detrimental excessive synapse elimination and contributing to synapse loss, which is the strongest neurobiological correlate of cognitive impairments in AD. Herein we review recent advances in characterizing complement-mediated synapse loss in AD, summarize the underlying mechanisms, and discuss the possible involvement of AD risk factors such as aging and various risk genes. We conclude with an overview of key questions that remain to be addressed.

Role of APOE in glaucoma

Glaucoma is a chronic blinding eye disease caused by the progressive loss of retinal ganglion cells (RGCs). Currently, no clinically approved treatment can directly improve the survival rate of RGCs. The Apolipoprotein E (APOE) gene is closely related to the genetic risk of numerous neurodegenerative diseases and has become a hot topic in the field of neurodegenerative disease research in recent years. The optic nerve and retina are extensions of the brain's nervous system. The pathogenesis of retinal degenerative diseases is closely related to the degenerative diseases of the nerves in the brain. APOE consists of three alleles, ε4, ε3, and ε2, in a single locus. They have varying degrees of risk for glaucoma. APOE4 and the APOE gene deletion (APOE-/-) can reduce RGC loss. By contrast, APOE3 and the overall presence of APOE genes (APOE+/+) result in significant loss of RGC bodies and axons, increasing the risk of glaucoma RGCs death. Currently, there is no clear literature indicating that APOE2 is beneficial or harmful to glaucoma. This study summarises the mechanism of different APOE genes in glaucoma and speculates that APOE targeted intervention may be a promising method for protecting against RGCs loss in glaucoma.

Specific serum autoantibodies predict the development and progression of Alzheimer's disease with high accuracy

Autoimmunity plays a key role in the pathogenesis of Alzheimer's disease (AD). However, whether autoantibodies in peripheral blood can be used as biomarkers for AD has been elusive. Serum samples were obtained from 1,686 participants, including 767 with AD, 146 with mild cognitive impairment (MCI), 255 with other neurodegenerative diseases, and 518 healthy controls. Specific autoantibodies were measured using a custom-made immunoassay. Multivariate support vector machine models were employed to investigate the correlation between serum autoantibody levels and disease states. As a result, seven candidate AD-specific autoantibodies were identified, including MAPT, DNAJC8, KDM4D, SERF1A, CDKN1A, AGER, and ASXL1. A classification model with high accuracy (area under the curve (AUC) = 0.94) was established. Importantly, these autoantibodies could distinguish AD from other neurodegenerative diseases and out-performed amyloid and tau protein concentrations in cerebrospinal fluid in predicting cognitive decline (P < 0.001). This study indicated that AD onset and progression are possibly accompanied by an unappreciated serum autoantibody response. Therefore, future studies could optimize its application as a convenient biomarker for the early detection of AD.

Alzheimer's Disease and Cancer: Common Targets

There is growing epidemiologic evidence of an inverse association between cancer and AD. In addition, both cell survival and death are regulated by the same signaling pathways, and their abnormal regulation may be implicated in the occurrence and development of cancer and AD. Research shows that there may be a common molecular mechanism between cancer and AD. This review will discuss the role of GSK3, DAPK1, PP2A, P53 and CB2R in the pathogenesis of cancer and AD and describe the current research status of drug development based on these targets.

Infectious Diseases

Microglia, brain-resident innate immune cells, have been extensively studied in neurodegenerative contexts like Alzheimer's disease. The Coronavirus disease 2019 (COVID-19) pandemic highlighted how peripheral infection and inflammation can be detrimental to the neuroimmune milieu and initiate microgliosis driven by peripheral inflammation. Microglia can remain deleterious to brain health by sustaining inflammation in the central nervous system even after the clearance of the original immunogenic agents. In this chapter, we discuss how pulmonary infection with Severe Acute Respiratory Syndrome CoronaVirus 2 (SARS-CoV-2) can lead to neurovascular and neuroimmune inflammation causing the neurological syndrome of post-acute sequelae of COVID-19 (PASC). Further, we incorporate lessons from the Human Immunodeficiency Virus' (HIV's) effects on microglial functioning in the era of combined antiretroviral therapies (cART) that contribute to HIV-1 associated neurocognitive disorders (HAND). Finally, we describe roles for mixed lineage kinase 3 (MLK3) and leucine-rich repeat kinase (LRRK2) as key regulators of multiple inflammatory and apoptotic pathways important to the pathogenesis of PASC and HAND. Inhibition of these pathways provides a therapeutically synergistic method of treating both PASC and HAND.

Contextualizing the Role of Osteopontin in the Inflammatory Responses of Alzheimer's Disease

Alzheimer's disease (AD) is characterized by progressive accumulations of extracellular amyloid-beta (Aβ) aggregates from soluble oligomers to insoluble plaques and hyperphosphorylated intraneuronal tau, also from soluble oligomers to insoluble neurofibrillary tangles (NFTs). Tau and Aβ complexes spread from the entorhinal cortex of the brain to interconnected regions, where they bind pattern recognition receptors on microglia and astroglia to trigger inflammation and neurotoxicity that ultimately lead to neurodegeneration and clinical AD. Systemic inflammation is initiated by Aβ's egress into the circulation, which may be secondary to microglial activation and can confer both destructive and reparative actions. Microglial activation pathways and downstream drivers of Aβ/NFT neurotoxicity, including inflammatory regulators, are primary targets for AD therapy. Osteopontin (OPN), an inflammatory cytokine and biomarker of AD, is implicated in Aβ clearance and toxicity, microglial activation, and inflammation, and is considered to be a potential therapeutic target. Here, using the most relevant works from the literature, we review and contextualize the evidence for a central role of OPN and associated inflammation in AD.

Alzheimer's disease: The role of proteins in formation, mechanisms, and new therapeutic approaches

Alzheimer's disease (AD) is a progressive neurological disorder that affects the central nervous system (CNS), leading to memory and cognitive decline. In AD, the brain experiences three main structural changes: a significant decrease in the quantity of neurons, the development of neurofibrillary tangles (NFT) composed of hyperphosphorylated tau protein, and the formation of amyloid beta (Aβ) or senile plaques, which are protein deposits found outside cells and surrounded by dystrophic neurites. Genetic studies have identified four genes associated with autosomal dominant or familial early-onset AD (FAD): amyloid precursor protein (APP), presenilin 1 (PS1), presenilin 2 (PS2), and apolipoprotein E (ApoE). The formation of plaques primarily involves the accumulation of Aβ, which can be influenced by mutations in APP, PS1, PS2, or ApoE genes. Mutations in the APP and presenilin (PS) proteins can cause an increased amyloid β peptides production, especially the further form of amyloidogenic known as Aβ42. Apart from genetic factors, environmental factors such as cytokines and neurotoxins may also have a significant impact on the development and progression of AD by influencing the formation of amyloid plaques and intracellular tangles. Exploring the causes and implications of protein aggregation in the brain could lead to innovative therapeutic approaches. Some promising therapy strategies that have reached the clinical stage include using acetylcholinesterase inhibitors, estrogen, nonsteroidal anti-inflammatory drugs (NSAIDs), antioxidants, and antiapoptotic agents. The most hopeful therapeutic strategies involve inhibiting activity of secretase and preventing the β-amyloid oligomers and fibrils formation, which are associated with the β-amyloid fibrils accumulation in AD. Additionally, immunotherapy development holds promise as a progressive therapeutic approach for treatment of AD. Recently, the two primary categories of brain stimulation techniques that have been studied for the treatment of AD are invasive brain stimulation (IBS) and non-invasive brain stimulation (NIBS). In this article, the amyloid proteins that play a significant role in the AD formation, the mechanism of disease formation as well as new drugs utilized to treat of AD will be reviewed.

siRNA drug delivery across the blood-brain barrier in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease with a few FDA-approved drugs that provide modest symptomatic benefits and only two FDA-approved disease-modifying treatments for AD. The advancements in understanding the causative genes and non-coding sequences at the molecular level of the pathophysiology of AD have resulted in several exciting research papers that employed small interfering RNA (siRNA)-based therapy. Although siRNA is being sought by academia and biopharma industries, several challenges still need to be addressed. We comprehensively report the latest advances in AD pathophysiology, druggable targets, ongoing clinical trials, and the siRNA-based approaches across the blood-brain barrier for addressing AD. This review describes the latest delivery systems employed to address this barrier. Critical insights and future perspectives on siRNA therapy for AD are also provided.

Neuronal ApoE4 in Alzheimer's disease and potential therapeutic targets

The most prevalent genetic risk factor for Alzheimer's disease (AD) is Apolipoprotein E (ApoE), a gene located on chromosome 19 that encodes three alleles (e2, e3, and e4) that give rise to the ApoE subtypes E2, E3, and E4, respectively. E2 and E4 have been linked to increased plasma triglyceride concentrations and are known to play a critical role in lipoprotein metabolism. The prominent pathological features of AD mainly include senile plaques formed by amyloid β (Aβ₄₂) aggregation and neuronal fibrous tangles (NFTs), and the deposited plaques are mainly composed of Aβ hyperphosphorylation and truncated head. In the central nervous system, the ApoE protein is primarily derived from astrocytes, but ApoE is also produced when neurons are stressed or affected by certain stress, injury, and aging conditions. ApoE4 in neurons induces Aβ and tau protein pathologies, leading to neuroinflammation and neuronal damage, impairing learning and memory functions. However, how neuronal ApoE4 mediates AD pathology remains unclear. Recent studies have shown that neuronal ApoE4 may lead to greater neurotoxicity, which increases the risk of AD development. This review focuses on the pathophysiology of neuronal ApoE4 and explains how neuronal ApoE4 mediates Aβ deposition, pathological mechanisms of tau protein hyperphosphorylation, and potential therapeutic targets.

APOEε4 and risk of Alzheimer's disease - time to move forward

The inheritance of Apolipoprotein E4 (APOEε4) brings the highest genetic risk of Alzheimer's disease (AD), arguably the highest genetic risk in human pathology. Since the discovery of the association, APOE protein isoforms have been at the center of tens of thousands of studies and reports. While, without a doubt, our knowledge about the normal physiological function of APOE isoforms in the brain has increased tremendously, the questions of how the inheritance of the APOEε4 allele translates into a risk of AD, and the risk is materialized, remain unanswered. Moreover, the knowledge about the risk associated with APOEε4 has not helped design a meaningful preventative or therapeutic strategy. Animal models with targeted replacement of Apoe have been generated and, thanks to the recent NIH/NIA/Alzheimer's disease Association initiative, are now freely available to AD researchers. While helpful in many aspects, none of the available models recapitulates normal physiological transcriptional regulation of the human APOE gene cluster. Changes in epigenetic regulation of APOE alleles in animal models in response to external insults have rarely been if ever, addressed. However, these animal models provide a useful tool to handle questions and investigate protein-protein interactions with proteins expressed by other recently discovered genes and gene variants considered genetic risk factors of AD, like Triggering Receptor expressed on Myeloid cells 2 (TREM2). In this review, we discuss genetic and epigenetic regulatory mechanisms controlling and influencing APOE expression and focus on interactions of APOE and TREM2 in the context of microglia and astrocytes' role in AD-like pathology in animal models.

Suppression of Wnt/β-Catenin Signaling Is Associated with Downregulation of Wnt1, PORCN, and Rspo2 in Alzheimer's Disease

Wnt and R-spondin (Rspo) proteins are two major types of endogenous Wnt/β-catenin signaling agonists. While Wnt/β-catenin signaling is greatly diminished in Alzheimer's disease (AD), it remains to be elucidated whether the inhibition of this pathway is associated with dysregulation of Wnt and Rspo proteins. By analyzing temporal cortex RNA-seq data of the human postmortem brain samples, we found that WNT1 and RRPO2 were significantly downregulated in human AD brains. In addition, the expression of Wnt acyltransferase porcupine (PORCN), which is essential for Wnt maturation and secretion, was greatly deceased in these human AD brains. Interestingly, the lowest levels of WNT1, PORCN, and RSPO2 expression were found in human AD brains carrying two copies of APOE4 allele, the strongest genetic risk factor of late-onset AD. Importantly, there were positive correlations among the levels of WNT1, PORCN, and RSPO2 expression in human AD brains. Supporting observations in humans, Wnt1, PORCN, and Rspo2 were downregulated and Wnt/β-catenin signaling was diminished in the 5xFAD amyloid model mice. In human APOE-targeted replacement mice, downregulation of WNT1, PORCN, and RSPO2 expression was positively associated with aging and APOE4 genotype. Finally, WNT1 and PORCN expression and Wnt/β-catenin signaling were inhibited in human APOE4 iPSC-derived astrocytes when compared to the isogenic APOE3 iPSC-derived astrocytes. Altogether, our findings suggest that the dysregulations of Wnt1, PORCN, and Rspo2 could be coordinated together to diminish Wnt/β-catenin signaling in aging- and APOE4-dependent manners in the AD brain.

An AS-qPCR-based method for the detection of Alzheimer's disease-related SNPs

Alzheimer's disease (AD) is one of the most serious neurodegenerative diseases in the world and has a strong genetic predisposition. At present, there is still no effective method for the early diagnosis and prevention of AD. Accumulating evidence shows the association of several loci with AD risk, such as apolipoprotein E (APOE) and translocase of outer mitochondrial membrane 40 (TOMM40). However, for routine disease diagnosis in clinics, genotype detection methods based on gene sequencing technology are time-consuming and excessively costly. Thus, in this study, we developed a high-sensitivity, low-cost, and convenient single nucleotide polymorphism (SNP) detection assay method based on allele-specific quantitative polymerase chain reaction (AS-qPCR) technology, which can be used to determine the SNP genotype in APOE and TOMM40. A total of 40 patients were recruited from the outpatient department of the memory clinic of Dongzhimen Hospital, Beijing University of Chinese Medicine. The SNP detection assay method includes three steps. First, positive plasmids with different genotypes (TT/CC/TC) in APOE rs429358, rs7412, and TOMM40 rs11556505 were prepared. Second, 3'-T/3'-C primers were designed to amplify these positive plasmids for each SNP site. Finally, we calculated the log10 of the copy number ratio for each positive plasmid, and the genotype interpretation interval was established. Based on this method, we investigated whether the SNPs in 40 patients could be accurately calculated using AS-qPCR technology. The accuracy of SNP detection was verified by PCR-Pooling sequencing. The results showed that SNP genotypes assessed by AS-qPCR technology corresponded perfectly to the results obtained by conventional DNA sequencing. We have developed a genotype detection method for AD based on AS-qPCR, which can be performed easily, rapidly, accurately, and at low cost. The method will contribute to the early diagnosis of patients with late-onset Alzheimer's and the detection of large clinical samples in the future.

Protein misfolding and related human diseases: A comprehensive review of toxicity, proteins involved, and current therapeutic strategies

Most of the cell's chemical reactions and structural components are facilitated by proteins. But proteins are highly dynamic molecules, where numerous modifications or changes in the cellular environment can affect their native conformational fold leading to protein aggregation. Various stress conditions, such as oxidative stress, mutations and metal toxicity may cause protein misfolding and aggregation by shifting the conformational equilibrium towards more aggregation-prone states. Most of the protein misfolding diseases (PMDs) involve aggregation of protein. We have discussed such proteins like Aβ peptide, α-synuclein, amylin and lysozyme involved in Alzheimer's, Parkinson's, type II diabetes and non-neuropathic systemic amyloidosis respectively. Till date, all advances in PMDs therapeutics help symptomatically but do not prevent the root cause of the disease, i.e., the aggregation of protein involved in the diseases. Current efforts focused on developing therapies for PMDs have employed diverse strategies; repositioning pre-existing drugs as it saves time and money; natural compounds that are touted as potential drug candidates have an advantage of being taken in diet normally and will induce lesser side effects. This review also covers recently developed therapeutic strategies like antisense drugs and disaggregases which has yielded therapeutic agents that have transitioned from preclinical studies into human clinical trials.

The relationships between neuroglial and neuronal changes in Alzheimer's disease, and the related controversies II:

Since the original description of Alzheimer´s disease (AD), research into this condition has mainly focused on assessing the alterations to neurons associated with dementia, and those to the circuits in which they are involved. In most of the studies on human brains and in many models of AD, the glial cells accompanying these neurons undergo concomitant alterations that aggravate the course of neurodegeneration. As a result, these changes to neuroglial cells are now included in all the "pathogenic cascades" described in AD. Accordingly, astrogliosis and microgliosis, the main components of neuroinflammation, have been integrated into all the pathogenic theories of this disease, as discussed in this part of the two-part monograph that follows an accompanying article on gliopathogenesis and glioprotection. This initial reflection verified the implication of alterations to the neuroglia in AD, suggesting that these cells may also represent therapeutic targets to prevent neurodegeneration. In this second part of the monograph, we will analyze the possibilities of acting on glial cells to prevent or treat the neurodegeneration that is the hallmark of AD and other pathologies. Evidence of the potential of different pharmacological, non-pharmacological, cell and gene therapies (widely treated) to prevent or treat this disease is now forthcoming, in most cases as adjuncts to other therapies. A comprehensive AD multimodal therapy is proposed in which neuronal and neuroglial pharmacological treatments are jointly considered, as well as the use of new cell and gene therapies and non-pharmacological therapies that tend to slow down the progress of dementia.

Apolipoprotein E in Cardiometabolic and Neurological Health and Diseases

A preponderance of evidence obtained from genetically modified mice and human population studies reveals the association of apolipoprotein E (apoE) deficiency and polymorphisms with pathogenesis of numerous chronic diseases, including atherosclerosis, obesity/diabetes, and Alzheimer’s disease. The human APOE gene is polymorphic with three major alleles, ε2, ε3 and ε4, encoding apoE2, apoE3, and apoE4, respectively. The APOE gene is expressed in many cell types, including hepatocytes, adipocytes, immune cells of the myeloid lineage, vascular smooth muscle cells, and in the brain. ApoE is present in subclasses of plasma lipoproteins, and it mediates the clearance of atherogenic lipoproteins from plasma circulation via its interaction with LDL receptor family proteins and heparan sulfate proteoglycans. Extracellular apoE also interacts with cell surface receptors and confers signaling events for cell regulation, while apoE expressed endogenously in various cell types regulates cell functions via autocrine and paracrine mechanisms. This review article focuses on lipoprotein transport-dependent and -independent mechanisms by which apoE deficiency or polymorphisms contribute to cardiovascular disease, metabolic disease, and neurological disorders.

Neuroprotective Effects of Resveratrol by Modifying Cholesterol Metabolism and Aβ Processing in SAMP8 Mice

Cholesterol metabolism seems dysregulated and linked to amyloid-β (Aβ) formation in neurodegeneration, but the underlying mechanisms are poorly known. Resveratrol (RSV) is a polyphenol with antioxidant activity and neuroprotective properties. Here, we analyzed the effect of age and RSV supplementation on cholesterol metabolism in the brain and blood serum, and its potential link to Aβ processing, in SAMP8 mice—an animal model of aging and Alzheimer’s disease. In the brain, our results revealed an age-related increase in ApoE and unesterified cholesterol in the plasma membrane whereas LDL receptor, HMG-CoA reductase, HMG-CoA-C1 synthase, and ABCA1 transporter remained unaltered. Furthermore, BACE-1 and APP gene expression was decreased. This dysregulation could be involved in the amyloidogenic processing pathway of APP towards Aβ formation. In turn, RSV exhibited an age-dependent effect. While levels of unesterified cholesterol in the plasma membrane were not affected by RSV, several participants in cholesterol uptake, release, and de novo synthesis differed, depending on age. Thus, RSV supplementation exhibited a different neuroprotective effect acting on Aβ processing or cholesterol metabolism in the brain at earlier or later ages, respectively. In blood serum, HDL lipoprotein and free cholesterol were increased by age, whereas VLDL and LDL lipoproteins remained unaltered. Again, the protective effect of RSV by decreasing the LDL or increasing the HDL levels also seems to depend on the intervention’s moment. In conclusion, age is a prominent factor for cholesterol metabolism dysregulation in the brain of SAMP8 mice and influences the protective effects of RSV through cholesterol metabolism and Aβ processing.